2,092 research outputs found
Construction and measurements of a vacuum-swing-adsorption radon-mitigation system
Long-lived alpha and beta emitters in the Rn decay chain on (and
near) detector surfaces may be the limiting background in many experiments
attempting to detect dark matter or neutrinoless double-beta decay, and in
screening detectors. In order to reduce backgrounds from radon-daughter
plate-out onto the wires of the BetaCage during its assembly, an
ultra-low-radon cleanroom is being commissioned at Syracuse University using a
vacuum-swing-adsorption radon-mitigation system. The radon filter shows
~20 reduction at its output, from 7.470.56 to 0.370.12
Bq/m, and the cleanroom radon activity meets project requirements, with a
lowest achieved value consistent with that of the filter, and levels
consistently < 2 Bq/m.Comment: 5 pages, 3 figures, Proceedings of Low Radioactivity Techniques (LRT)
2013, Gran Sasso, Italy, April 10-12, 201
Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy
Positive and negative streamers are studied in ambient air at 1 bar; they
emerge from a needle electrode placed 40 mm above a planar electrode. The
amplitudes of the applied voltage pulses range from 5 to 96 kV; most pulses
have rise times of 30 ns or shorter. Diameters, velocities and energies of the
streamers are measured. Two regimes are identified; a low voltage regime where
only positive streamers appear and a high voltage regime where both positive
and negative streamers exist. Below 5 kV, no streamers emerge. In the range
from 5 to 40 kV, positive streamers form, while the negative discharges only
form a glowing cloud at the electrode tip, but no streamers. For 5 to 20 kV,
diameters and velocities of the positive streamers have the minimal values of
d=0.2 mm and v \approx 10^5 m/s. For 20 to 40 kV, their diameters increase by a
factor 6 while the voltage increases only by a factor 2. Above the transition
value of 40 kV, streamers of both polarities form; they strongly resemble each
other, though the positive ones propagate further; their diameters continue to
increase with applied voltage. For 96 kV, positive streamers attain diameters
of 3 mm and velocities of 4*10^6 m/s, negative streamers are about 20 % slower
and thinner. An empirical fit formula for the relation between velocity v and
diameter d is v=0.5 d^2/(mm ns) for both polarities. Streamers of both
polarities dissipate energies of the order of several mJ per streamer while
crossing the gap.Comment: 20 pages, 9 figures, accepted for J. Phys.
Specific heat at the transition in a superconductor with fluctuating magnetic moments
In the heavy-fermion materials CeCoIn and UBe, the superconducting
order parameter is coupled to flucutating magnetization of the uncompensated
part of the localized -moments. We find that this coupling decreases the
superconducting transition temperature and increases the jump of the
specific-heat coefficient, which indicates entropy transfer from the magnetic
to the superconducting degree of freedom at the transition temperature. Below
the transition, we find that the magnetic fluctuations are suppressed. We
discuss the relation of our results to experiments on CeCoIn under
pressure.Comment: 4 pages, 1 figur
Investigation of Thermal and Vacuum Transients on the LHC Prototype Magnet String
The prototype magnet string, described in a companion paper, is a full-scale working model of a 50-m length of the future Large Hadron Collider (LHC), CERN's new accelerator project, which will use high-field superconducting magnets operating below 2 K in superfluid helium. As such, it provides an excellent test bed for practising standard operating modes of LHC insulation vacuum and cryogenics, as well as for experimentally assessing accidental behaviour and failure modes, and thus verifying design calculations. We present experimental investigation of insulation vacuum pumpdown, magnet forced-flow cooldown and warmup, and evolution of residual vacuum pressures and temperatures in natural warmup, as well as catastrophic loss of insulation vacuum. In all these transient modes, experimental results are compared with simulated behaviour, using a non-linear, one-dimensional thermal model of the magnet string
Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-d interfaces
We have studied quasiparticle tunneling into atomically flat a-axis films of
YBa2Cu3O7-d and DyBa2Cu3O7-d through epitaxial CaTiO3 barriers. The junction
heterostructures were grown by oxide molecular beam epitaxy and were carefully
optimized using in-situ monitoring techniques, resulting in unprecedented
crystalline perfection of the superconductor/insulator interface. Below Tc, the
tunneling conductance shows the evolution of a large unexpected asymmetrical
feature near zero bias. This is evidence that superconducting YBCO crystals,
atomically truncated along the lobe direction with a titanate layer, have
intrinsically broken particle-hole symmetry over macroscopically large areas.Comment: 15 pages, 4 figures; v2 includes minor changes in concluding
paragraph to match PRL versio
Ontwikkeling biologische teelt en trek van witlof
In samenwerking tussen Proeftuin Zwaagdijk en PPO Lelystad werd in de jaren 2000-2002 een onderzoeksproject uitgevoerd met als doel de teeltzekerheid, opbrengst en kwaliteit van biologische witlof te vergroten. Onderzoek werd toegespitst op bemesting en bestrijding van onkruid tijdens de teelt van witlofpennen. In de trek werden verschillende soorten biologische meststoffen en rassen vergeleken
Algorithm for obtaining the gradient expansion of the local density of states and the free energy of a superconductor
We present an efficient algorithm for obtaining the gauge-invariant gradient
expansion of the local density of states and the free energy of a clean
superconductor. Our method is based on a new mapping of the semiclassical
linearized Gorkov equations onto a pseudo-Schroedinger equation for a
three-component wave-function psi(x), where one component is directly related
to the local density of states. Because psi(x) satisfies a linear equation of
motion, successive terms in the gradient expansion can be obtained by simple
linear iteration. Our method works equally well for real and complex order
parameter, and in the presence of arbitrary external fields. We confirm a
recent calculation of the fourth order correction to the free energy by
Kosztin, Kos, Stone and Leggett [Phys. Rev. B 58, 9365 (1998)], who obtained a
discrepancy with an earlier result by Tewordt [Z. Phys. 180, 385 (1964)]. We
also give the fourth order correction to the local density of states, which has
not been published before.Comment: 12 preprint pages, added remark concerning Eilenberger equation,
accepted for publication in Phys. Rev.
TRANSMIT: Training Research and Applications Network to Support the Mitigation of Ionospheric Threats
TRANSMIT is an initiative funded by the European Commission through a Marie Curie Initial Training Network (ITN). Main aim of such networks is to improve the career perspectives of researchers who are in the first five years of their research career in both public and private sectors. In particular TRANSMIT will provide a coordinated program of academic and industrial training, focused on atmospheric phenomena that can significantly impair a wide range of systems and applications that are at the core of several activities embedded in our daily life. TRANSMIT deals with the harmful effects of the ionosphere on these systems, which will become increasingly significant as we approach the next solar maximum, predicted for 2013. Main aim of the project is to develop real time integrated state of the art tools to mitigate ionospheric threats to Global Navigation Satellite Systems (GNSS) and several related applications, such as civil aviation, marine navigation and land transportation. The project will provide Europe with the next generation of researchers in this field, equipping them with skills developed through a comprehensive and coordinated training program. Theirs research projects will develop real time integrated state of the art tools to mitigate these ionospheric threats to GNSS and several applications that rely on these systems. The main threat to the reliable and safe operation of GNSS is the variable propagation conditions encountered by GNSS signals as they pass through the ionosphere. At a COST 296 MIERS (Mitigation of Ionospheric Effects on Radio Systems) workshop held at the University of Nottingham in 2008, the establishment of a sophisticated Ionospheric Perturbation Detection and Monitoring (IPDM) network (http://ipdm.nottingham.ac.uk/) was proposed by European experts and supported by the European Space Agency (ESA) as the way forward to deliver the state of the art to protect the range of essential systems vulnerable to these ionospheric threats. Through a set of carefully designed research work packages TRANSMIT will be the enabler of the IPDM network. The goal of TRANSMIT is therefore to provide a concerted training programme including taught courses, research training projects, secondments at the leading European institutions, and a set of network wide events, with summer schools, workshops and a conference, which will arm the researchers of tomorrow with the necessary skills and knowledge to set up and run the proposed service. TRANSMIT will count on an exceptional set of partners, encompassing both academia and end users, including the aerospace and satellite communications sectors, as well as GNSS system designers and service providers, major user operators and receiver manufacturers. TRANSMIT's objectives are: A. Develop new techniques to detect and monitor ionospheric threats, with the introduction of new prediction and forecasting models, mitigation tools and improved system design; B. Advance the physical modeling of the underlying processes associated with the ionospheric plasma environment and the knowledge of its influences on human activity; C. Establish a prototype of a real time system to monitor the ionosphere, capable of providing useful assistance to users, which exploits all available resources and adds value for European services and products; D. Incorporate solutions to this system that respond to all end user needs and that are applicable in all geographical regions of European interest (polar, high and mid-latitudes, equatorial region). TRANSMIT will pave the way to establish in Europe a system capable of mitigating ionospheric threats on GNSS signals in real tim
Temperature dependence of the magnetic anisotropy of metallic Y-Ba-Cu-O single crystals in the normal phase
The magnetic anisotropy measurements of metallic Y-Ba-Cu-O compounds in the normal phase reveal a temperature-dependent diamagnetic component of the susceptibility that increases with decreasing temperature. The temperature variation of the susceptibility anisotropy and its total change do not seem to be much affected by the presence of the superconductivity at some lower temperature and could not be accounted for by superconducting fluctuations. Rather, the data remind one of the behavior of some quasi-two-dimensional metals with anisotropic Fermi surfaces, reflecting the properties of the low-energy excitations in the normal phase. The anisotropy measurements above the bulk superconducting transition temperature Tc reveal the nonlinear effects, which are due to the onset of superconductivity in disconnected grains. The existence of a two-step transition, typical for granular superconductors, should be taken into consideration if the normal-phase susceptibility data are compared with the theoretical predictions in the vicinity of Tc
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